Organic materials, whether natural or synthetic, are conventionally protected against degradation by ultraviolet (UV) light by incorporating a UV light stabilizer in the material. Many classes of compounds are known to be useful UV light stabilizers, some being more effective than others. Particularly effective 2-keto-diazacycloalkanes which provide stabilized compositions resistant to degradation by UV light, include the 2-keto-1,4-diazacycloalkanes disclosed in U.S. Pat. No. 4,190,571; and, the 2-keto-1,5-diazacycloalkanes disclosed in U.S. Pat. No. 4,207,228. Other 2-keto-diazacycloalkanes useful as UV light stabilizers are disclosed in U.S. Pat. Nos. 3,919,234; 3,920,659; and 3,928,330 which teach substituted piperazinediones. Cycloalkanes useful as UV light stabilizers are disclosed in Ger. Offen. No. 2,315,042; Japanese Pat. Nos. 7,453,571 and 7,453,572.
The compounds of this invention belong to a the general class of compounds known as hindered amines. Hindered amines, to which general class the compounds of the invention belong, are known to have utility as u-v light stabilizers in synthetic resins subject to actinic radiation. However, not all hindered amines are effective stabilizers against u-v light degradation in normally solid polymers. Some hindered amines are thermally unstable at as low as 100.degree. C. which precludes their use in any organic material which is processed at or above that temperature. Further, particularly with polysubstituted heterocyclic ring compounds, N atoms in the ring are known to have a beneficial effect but there is no logical reason to expect that an oligomer may be formed which has relatively few repeating units of a polyisocyanate which are self-limiting to just about the right number so as to provide a desirable molecular weight; nor is there any reason to expect that a peculiar structure of two distally linked polysubstituted 2-keto-1,4-diazacycloalkane ("2KDZC") moieties, themselves distally linked, would, in conjunction with a polymeric isocyanate, provide better stabilization activity than either the 2KDZC Bis compound, or the polymeric isocyanate (also termed "urethane oligomer"). By "distally linked" we refer to bridging or linking by at least 2 carbon atoms.
Because of the unpredictability of the effectiveness of various hindered amines solely based on their (hindered) structure, much effort has been expended to synthesize hindered amines which must then be tested for possible utility as u-v light stabilizers. One of the synthesis is described in an article titled "Hindered Amines. Novel Synthesis of 1,3,3,5,5-Pentasubstituted 2-Piperazinones" by John T. Lai in J. Org. Chem. 45, 754 (1980).
Hindered amines of the prior art are generally complex compounds not prepared with notable ease, and their properties, particularly their compatibility in various synthetic resins, is difficult to predict. Apparently small differences in structure, result in large differences in performance. Prolonged efforts to provide simpler compounds which are relatively easily prepared, have resulted in the 2-keto-1,4-diazacycloalkanes and the 2-keto-1,5-diazacycloalkanes disclosed in U.S. Pat. Nos. 4,190,571 and 4,207,228.
The key to the ubiqutous presence of "hindered amine" u-v light stabilizers is the relative ease with which they are commercially prepared, compared with u-v stabilizers having comparable activity but different structures. Currently available, relatively easily prepared u-v stabilizers include for example, Tinuvin.RTM.622 which is a succinate ester of a polysubstituted piperidine, more fully disclosed in U.S. Pat. Nos. 4,233,410 and 4,233,412; Tinuvin.RTM.770 which is a triazine substituted with piperidine substituents; and, Chimasorb.RTM.944 which has a polytriazine structure with piperidine substituents, as disclosed in U.S. Pat. No. 4,086,204. However, the aforementioned stabilizers are relatively easily extracted from prior art u-v stabilized compositions. This invention derives from the discovery that changes in structure of a hindered amine are effective to improve not only the ease with which they may be prepared and thus be inexpensive, but also to improve their extraction from organic polymers, thus giving the polymers longer lasting protection against degradation by u-v light.
The present invention further derives from research in the field of the synthesis of hindered amines having peculiar structural characteristics, and an evaluation of their effectiveness as u-v light stabilizers. The concept of retaining the "2-keto" ring structure of a heterocyclic ring containing at least one N atom was the basis upon which the search for effective polymers containing this structure was initiated. The practicality of providing more than two substituents on the N-adjacent C atoms of a 2-keto-1,4-diazacycloalkane derives from the discovery of the "ketoform synthesis" disclosed in U.S. Pat. No. 4,167,512; the "cyanohydrin acetate synthesis" disclosed in U.S. Pat. No. 4,240,961; and, the "soft ion catalyst synthesis" disclosed in U.S. Pat. No. 4,246,412; other preparations of 2-keto-1,4-diazacycloalkanes, particularly bis compounds thereof, disclosed in U.S. Pat. Nos. 4,190,571; 4,292,240; 4,297,497; and 4,309,336 inter alia; and the disclosures of each of the foregoing patents are incorporated by reference thereto as if fully set forth herein. The retention of the 2-keto structure in a diazacycloalkane bis compound which links at least two urethane moieties, spurred the discovery of the novel polysubstituted 2-keto-1,4-diazacycloalkane-urethane ("2K-U" for brevity) oligomers of this invention as highly effective u-v stabilizers in novel compositions.